1. Field of the Invention
Embodiments of the present invention relates to a liquid crystal display panel, and more particularly to a liquid crystal display panel for a liquid crystal display device. Embodiments of the invention are suitable for a wide scope of applications. In particular, embodiments of the invention are suitable for driving a liquid crystal panel to improve an image quality of a liquid crystal display device having the same.
2. Description of the Related Art
The development of information-driven society leads to a high demand for various forms of display devices. Examples of these display devices include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, and electro luminescence (EL) display device. In particular, the LCD device, which provides excellent image quality, is light, compact, consumes low power, and can display full color images. Accordingly, the LCD device is widely displacing the cathode ray tube (CRT) as a display of choice. For example, LCD devices are as monitors for car navigation, portable devices, and television.
FIG. 1 shows a circuit diagram of a liquid crystal panel according to the related art. Referring to FIG. 1, a liquid crystal panel 2 includes a plurality of gate lines GL1 to GL3 in a first direction, and a plurality of data lines DL1 to DL3 in a second direction on a first substrate (not shown). The gate lines GL1 to GL3 cross the data lines DL1 to DL3. Pixel regions P are defined by crossings of the gate lines GL1 to GL3 and the data lines DL1 to DL3. The pixel regions P form a matrix on the first substrate of the liquid crystal panel. Thin film transistors (TFTs) and pixel electrodes are formed in each pixel region P of the first substrate. A plurality of common lines VL1 to VL3 are provided in parallel with the gate lines GL1 to GL3, respectively on the first substrate.
Various color filters are disposed in a second substrate (not shown) facing the first substrate to correspond to the pixel regions P. A liquid crystal material (not shown) is interposed between the first substrate and the second substrate.
A plurality of common electrodes are formed in each of the pixel region P diverging from the common line VL1 to VL3. The common electrodes are formed in the pixel regions P in parallel with the pixel electrodes. The common electrodes are electrically connected to the common lines VL1 to VL3.
Each of the pixel electrodes and the common lines overlaps to form a storage capacitance Cst. The storage capacitance Cst maintains a data voltage supplied to the pixel electrode during one frame period. Additionally, a liquid crystal capacitance Clc is formed by the liquid crystal material between the pixel electrode and the common electrode. The liquid crystal capacitance Clc maintains an electric potential difference between the data voltage supplied to the liquid crystal and a common voltage of the common electrode.
The TFT is turned on by a scan signal supplied to the gate lines GL1 to GL3 of the liquid crystal. A data voltage supplied to the data lines DL1 to DL3 is applied to the pixel electrode through the TFT. A common voltage supplied to the common lines VL1 to VL3 is applied to the common electrode. An electric field is generated by an electric potential difference between the data voltage and the common voltage. A desired image is displayed by changing an optical characteristics of the liquid crystal material in accordance with the generated electric field.
The data voltage supplied to the liquid crystal panel 2 can be periodically inverted to prevent afterimages and flickers. The inverted data voltage is supplied between dots, lines, or frames. For example, a positive polarity data voltage having a higher level than the common voltage is supplied during a first time period. Then, the data voltage is inverted during a second time period by supplying a negative polarity data voltage having a lower level than the common voltage. The positive polarity data voltage and the negative polarity data voltage are alternately supplied.
FIG. 2 is a voltage waveform applied to the liquid crystal panel of FIG. 1. Referring to FIG. 2, the scan signal applied to the gate line supplies a gate high voltage VGH having a higher level during one horizontal period H in one frame period, and a gate low voltage VGL having a low level during the remaining part of the frame period. Accordingly, the TFT is turned on by the gate high voltage VGH and is turned off by the gate low voltage VGL.
When the gate high voltage VGH is inverted into the gate low voltage VGL, the TFT is turned off, and a data voltage Vd charged in the pixel electrode causes a voltage drop, such as a kick-back voltage ΔVp. Accordingly, the data voltage Vd, which drops by an amount corresponding to the kick-back voltage ΔVp, is charged in the pixel electrode.
The kick-back voltage ΔVp is expressed as Equation (1):
                              Δ          ⁢                                          ⁢                      V            p                          =                                            C              gs                                                      C                gs                            +                              C                st                            +                              C                lc                                              ⁢                      (                                          V                GH                            -                              V                GL                                      )                                              (        1        )            where ΔVp represents a kick-back voltage. Cgs denotes a capacitor between a gate electrode and a source electrode in TFT, Cst denotes a storage capacitor, Clc denotes a liquid crystal capacitor. VGH and VGL represent a gate high voltage and a gate low voltage, respectively.
In the related art LCD device, the kick-back voltage ΔVp occurs in a positive polarity data voltage and a negative polarity data voltage. In this case, although the positive polarity data voltage and the negative polarity data voltage have an identical grayscale, the common voltage does not have an intermediate value. Thus, flickers occur because an identical grayscale can not produced. The common voltage needs to be tuned to prevent these flickers.
Additionally, since a gamma voltage value needs to be tuned to prevent the flickers, an additional unit, such as a tuner, is required to tune the gamma voltage value. Therefore, the gamma voltage generator becomes complicated, and increases in size.
Moreover, the related art gamma voltage generator includes a positive polarity gamma voltage generator generating a gamma voltage corresponding to white, and a negative polarity gamma voltage generator for generating a gamma voltage corresponding to black. Thus, the related art LCD device requires two different gamma voltage generators white and black, a circuit of a gamma voltage generator becomes more complicated, and its size increases more.